We propose to study key cellular processes related to the tropic actions of ACTH and LH on steroidogenesis in rat adrenocortical carcinoma cells and rat Leydig tumor cells respectively. We shall investigate: (1) The ACTH and LH-promoted uptake and utilization of high density lipoprotein cholesterol for increased steroidogenesis, with special emphasis on the determination of the importance of the non-esterified cholesterol component of the lipoprotein as a steroidogenic precursor in isolated adrenocortical carcinoma and Leydig tumor cells; (2) the contribution of ACTH or LH-independent steroidogenesis from "de novo" synthesized cholesterol to overall steroid production and the apparent lack of inhibition of cholesterol biosynthesis by lipoproteins in adrenal carcinoma tissue; (3) the isolation and purification of protein(s) from adrenal tumor cell cytosol that may be involved in the intracellular transportation of cholesterol from the sites of uptake to the mitochondrial site of sterol metabolism. We shall determine whether ACTH or LH alters the amount and subcellular distribution of cholesterol-binding protein in adrenal and testicular Leydig tumor cells, using immune precipitation techniques for quantification. The overall objective of our studies is to understand the biochemical events occurring at the cellular level during tropic hormonal stimulation of tumor cells of rat adrenal and testis that have very limited cholesterol ester metabolism. Such studies may lead to an understanding and control of the massive steroid secretion of adrenocortical and testicular Leydig cell carcinomas.